1. Field of the Invention
This invention relates to a method of modifying the wettability of glass beads, to glass beads, to a synthetic polymeric matrix incorporating glass beads, and to a method of applying a reflective marking to a surface.
2. Description of the Background
The present invention is principally concerned with the properties of glass beads which are to be incorporated into a polymeric matrix and which contact the material which is to form the matrix while that material is in the liquid state. The material which is to form the matrix may be in the form of a melt, a solution, or a dispersion, and it may be polymeric or polymerisable.
Glass beads may be incorporated into synthetic polymeric material for a variety of purposes, for example as fillers in thermoplastics materials and in thermosetting resins in order to modify the properties of the material or to facilitate moulding, and in order to give light-reflecting properties to paints. When used as filler in thermoplastics and thermosetting materials, it is often desirable that the beads should be evenly distributed throughout the final product in order to give uniformity of properties, and this implies that the beads should be uniformly distributed in the liquid material from which the product is moulded. Even where uniform distribution is not desired, it is in general true to say that there will be some optimum distribution of the filler material in the finished product and thus in the liquid from which it is moulded.
Certain analogous problems arise in connexion with paints which may be applied to form road markings, for example to divide a carriageway into different traffic lanes or to indicate traffic priorities at road junctions. It is desirable that such markings should be highly visible at night, and one way of promoting high visibility is to incorporate glass beads into the markings to reflect light from a vehicle's lamps back to the driver of that vehicle. It will of course be appreciated that in order to exhibit this effect, at least some of the glass beads must be well exposed at the surface of the marking. If the beads are exposed, there is a risk that they may be removed as traffic is driven over the marking, with the result that during the course of time, more and more beads are removed so that the marking becomes less and less reflective and so less clearly visible at night. It is therefore desirable that the beads should be distributed through the thickness of the paint in order to maintain such reflectivity for as long as possible. On the other hand, if reflective paint is to be used in circumstances where it will not be exposed to such a degree of wear, for example as in road signs, it is desirable that the beads should be mainly at the surface of the paint, though sufficiently well bonded to it to resist weathering.
It is an object of the present invention to provide a method of modifying the wettability of glass beads so as to render them especially suitable for use as referred to above.